This invention relates to an improvement in a method of configuring a vehicle assembly line for assembling vehicle bodies of different models by takt time control.
It has been attempted on vehicle assembly lines to reduce the number of assembly lines and consolidate operations by making a plurality of vehicles of different models (model xe2x80x9cAxe2x80x9d, model xe2x80x9cBxe2x80x9d) flow in a common line and doing assembly there, which is called a mixed-model process. As an invention related to the mixed-model process, Japanese Patent No. 2920801 entitled xe2x80x9cTransferring Method for Vehicle Assembly Line,xe2x80x9d for example, is known.
In this transferring method, a plurality of vehicles of each of model xe2x80x9cAxe2x80x9d and model xe2x80x9cB,xe2x80x9d which models are different in the number of assembling processes, are aligned in a vehicle group, and the vehicles of models xe2x80x9cAxe2x80x9d and xe2x80x9cBxe2x80x9d in groups sequentially flow in the assembly line. When model xe2x80x9cAxe2x80x9d has a larger number of assembling processes than model xe2x80x9cB,xe2x80x9d the line speed is switched to a long takt time, that is, a low speed, immediately before a vehicle of model xe2x80x9cAxe2x80x9d comes into the assembly line. While a vehicle(s) of model xe2x80x9cAxe2x80x9d are present in the assembly line, the assembly line is maintained in the long takt time. When all vehicles of model xe2x80x9cAxe2x80x9d have gone out from the line exit and the assembly line has no vehicles of model xe2x80x9cAxe2x80x9d but vehicles of model xe2x80x9cB,xe2x80x9d the assembly line is switched to a short takt time, that is, the line speed is switched to a high speed. This leads to increased productivity.
In the mixed-model assembling process of the above publication in which both vehicles of model xe2x80x9cAxe2x80x9d which take time in assembly and vehicles or model xe2x80x9cBxe2x80x9d which are relatively easily assembled are processed, the processing is performed in a long takt time when a vehicle(s) of model xe2x80x9cAxe2x80x9d are in the line, and is performed in a short takt time when only vehicles of model xe2x80x9cBxe2x80x9d are in the line. As compared with a case where the assembly line is operated at the line speed of only a long takt time, the operation of the assembly line at two speeds of long and short takt times as in the above publication increases an average line speed, thereby increasing productivity by the increased amount.
However, when only one vehicle of a model having a larger number of assembling processes is present in the assembly line, the long takt time should be selected, preventing much increase in the effect of increasing the average line speed.
It is thus an object of the present invention to provide a method of configuring an assembly line which enables increase in the line speed when certain conditions are satisfied even with a vehicle(s) of a model having a larger number of assembly man-hours (a larger number of assembly processes) present in the assembly line.
According to a first aspect of the present invention, there is provided a method of configuring a vehicle assembly line through which vehicle bodies of a plurality of different models having undergone painting are transferred, during which components are sequentially installed, inspected, and repaired as necessary, to provide finished vehicles, which method comprises the steps of: grouping the components to be installed based on mounting positions, installing procedures, and functions thereof so as to divide the vehicle assembly line into at least three zones; setting standard assembly man-hours common for the different models for each divided zone; comparing the standard assembly man-hours with assembly man-hours of each zone for each model; and laying side by side a zone having a largest number of assembly man-hours and a zone having a second largest number of assembly man-hours.
Thus dividing the vehicle assembly line into the at least three zones, setting the average assembly man-hours or each zone, comparing the average assembly man-hours with assembly man-hours of each zone for each model, and laying side by side a zone having a largest number of assembly man-hours and a zone having a second largest number of assembly man-hours enable the adoption of a middle takt time which is intermediate between a long takt time and a short takt time.
The above method of configuring a vehicle assembly line preferably further comprises the step of setting the vehicle assembly line to run in a long takt time when vehicles of a model having a larger number of assembly man-hours are present in the zones having the first and second largest numbers of assembly man-hours, and to run in a middle takt time when a vehicle of a model having a larger number of assembly man-hours is present in any zone other than the zones having the first and second largest numbers of assembly man-hours, and to run in a short takt time when no vehicles of a model having a larger number of assembly man-hours are present in the assembly line. This enables fine takt time selection, increasing productivity.
The at least three zones preferably comprise a wiring/piping and communication equipment zone, an interior equipment zone, an underside equipment zone, an exterior equipment zone, and a complex quality assurance zone.
In a preferred embodiment, the above method of configuring a vehicle assembly line further comprises the step of calculating man-hour ratios as the assembly man-hours of the respective zones for each of the different models prior to the comparing step, wherein the top two ranks in the man-hour ratios of one of the models having a larger number of assembly man-hours correspond to the wiring/piping and communication equipment one and the interior equipment zone, and the next higher one of the man-hour ratios following the top two ranks corresponds to the underside equipment zone, and the exterior equipment zone and the complex quality assurance zone have a constant man-hour ratio lower than the man-hour ratios of the top three ranks, and therefore the wiring/piping and communication equipment zone and the interior equipment zone are first disposed side by side, and the underside equipment zone is disposed adjacent to these zones, followed by the disposition of the exterior equipment zone and the complex quality assurance zone.